The invention concerns a mortar based on clay and cement with a proportion by weight of clay greater than that of the cement, a mortar resulting in finished products which are at the same time inexpensive and of quality, in particular as regards their mechanical resistance and the substantial absence of cracking or shrinkage.
It also concerns methods of preparation and use of these mortars as well as the products made by means of the latter.
It will be recalled that it is already known for a mortar to be made by mixing or "gauging" clay, "gauging", water and certain mineral adjuvants such as sodium phosphates, sodium carbonate or calcium carbonate; these adjuvants exert in general a deflocculating or wetting effect, allowing the gauging water to dispense better in the mixture of clay and cement.
The inventors have discovered that such a deflocculating effect even if it perhaps facilitates the mixing itself, leads to mediocre characteristics of resistance and cohesion for the finished products after setting.
According to the invention, on the other hand, in addition to the gauging water, there is added to the clay-cement mixture a hydrophilic agent, capable of increasing the thixotropy of the mixture and crosslinking the product by polymerization during the subsequent setting, this agent being chosen from among urea-formaldehyde and melamine-formaldehyde resins and derivatives of ammonia such as formamide and being generally in solution in the gauging water, and this agent being used at a dry weight percentage between 1 and 20 based on the dry weight of the clay-cement mixture to which it is added.
It is also an object of the invention to improve the plasticity of the mortars concerned and to delay the setting thereof, which facilitates their application and in particular permits their injection into molds of small aperture such as pre-stressed sheaths.
In preferred embodiments use is made of one and/or other of the following features:
the proportion by weight of clay in the clay-cement mixture is between 1.5 and 4 times that of the cement, PA1 the clay used is basic [pH greater than 8] or rendered basic by the addition of silicates and/or of sodium aluminates, PA1 before mixing the clay with the cement, the quantity of absorbed water present in this clay is reduced by adding to it an additive, which is flocculant and/or capable of giving the clay water-repellent properties, in a proportion by dry weight of the order of 0.5 to 5 parts per thousand based on the dry weight of the clay, PA1 there is added, to one at least of the constituents of the mortar, aluminium powder in a proportion by dry weight of the order of 0.1 to 2 parts per thousand based on the dry weight of the said constituent, PA1 there is added, to the clay-cement mixture, a load of glass or the like in the form of fibres, powder or gel, PA1 there is added, to the clay-cement mixture, an acrylic of A.B.S. emulsion or the like, preferably diluted in water, at a dry solids weight percentage between 5 and 25% based on the dry weight of the clay-cement mixture, PA1 after use of the mortar according to the invention, the products made from this mortar are kept in an atmosphere saturated with water vapour for several hours before being slowly dried, PA1 paraffin is added to one of the constituants of the mortar, preferably to the powdered cement, the weight of this paraffin being comprised between 0.3 and 5% of the weight of the cement, PA1 the paraffin which is solid at ordinary temperature is melted and dissolved in an organic solvent composed preferably half of a hydrocarbon (e.g., gasoline, petroleum or white spirit) and half of acetone, the amount by weight of the paraffin being of the order of 2/3 of this solution, PA1 the paraffin solution according to the preceding paragraph is mixed directly with the powdered cement, PA1 the paraffin solution according to the second preceding paragraph is mixed with water, in a substantially equivalent amount, with the amino-resin constituting the additive, the creamy liquid obtained constituting the liquid component whose addition to the powdery clay-cement mixture enables the mortar to be constituted, PA1 there is added to the above-defined mortar simultaneously but separately, sodium aluminate and sodium silicate in substantially identicallproportions by weight, the amount by weight of these salts thus added to the mortar being comprised between 0.4 and 2% by weight of the dry components of the starting clay-cement powder.
The following features, used preferably in combination improve the plasticity of the mortars concerned and delay the setting thereof:
The invention involves, apart from these principal features, certain other features which are preferably used at the same time and which will be more explicityly mentioned thereafter.